Wireless communication devices such as mobile phone terminals may transmit and receive signals of a plurality of bands. For example, Long Term Evolution (LTE) or the like uses a Low Band (LB) equal to or less than 1 GHz, a Middle Band (MB) around 2 GHz, a High Band (HB) around 2.5 GHz, and a Very High Band (VHB) around 3.5 GHz. Each of the Low Band, the Middle Band, the High Band, and the Very High Band includes a plurality of bands each including a transmit band and a receive band.
International Publication No. 2011/004525 describes that a tunable duplexer is provided to support a plurality of bands. U.S. Patent Application Publication No. 2013/0273861 describes that a filter to be connected to an antenna is switched with a switch. International Publication No. 2015/128007 and U.S. Patent Application Publication No. 2014/0038531 describe that a tunable filter is used as a transmit filter and a receive filter. International Publication No. 2015/112673 describes that an impedance adjustment circuit is located between a filter and an antenna.
To support multiple bands, many filters are used. The use of a variable filter can reduce the number of filters. However, in the above-described documents, the number of filters are not efficiently reduced.